title: Arabidopsis CRY2 and ZTL mediate blue-light regulation of the transcription factor CIB1 by distinct mechanisms.
abstract: Plants possess multiple photoreceptors to mediate light regulation of growth and development, but it is not well understood how different photoreceptors coordinate their actions to jointly regulate developmental responses, such as flowering time. In Arabidopsis, the photoexcited cryptochrome 2 interacts with the transcription factor CRYPTOCHROME-INTERACTING basic helix-loop-helix 1 (CIB1) to activate transcription and floral initiation. We show that the CIB1 protein expression is regulated by blue light; CIB1 is highly expressed in plants exposed to blue light, but levels of the CIB1 protein decreases in the absence of blue light. We demonstrate that CIB1 is degraded by the 26S proteasome and that blue light suppresses CIB1 degradation. Surprisingly, although cryptochrome 2 physically interacts with CIB1 in response to blue light, it is not the photoreceptor mediating blue-light suppression of CIB1 degradation. Instead, two of the three light-oxygen-voltage (LOV)-domain photoreceptors, ZEITLUPE and LOV KELCH PROTEIN 2, but not FLAVIN-BINDING KELCH REPEAT 1, are required for the function and blue-light suppression of degradation of CIB1. These results support the hypothesis that the evolutionarily unrelated blue-light receptors, cryptochrome and LOV-domain F-box proteins, mediate blue-light regulation of the same transcription factor by distinct mechanisms.
authors.affiliation: National Key Laboratory of Plant Molecular Genetics, Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai 200032, China.
authors.forename: Hongtao
authors.initials: H
authors.lastname: Liu
authors.forename: Qin
authors.initials: Q
authors.lastname: Wang
authors.forename: Yawen
authors.initials: Y
authors.lastname: Liu
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Zhao
authors.forename: Takato
authors.initials: T
authors.lastname: Imaizumi
authors.forename: David E
authors.initials: DE
authors.lastname: Somers
authors.forename: Elaine M
authors.initials: EM
authors.lastname: Tobin
authors.forename: Chentao
authors.initials: C
authors.lastname: Lin
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics* / Q000378:metabolism; D056931:Cryptochromes / Q000235:genetics* / Q000378:metabolism; D035264:Flowers / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects*; D015151:Immunoblotting; D008027:Light; D030821:Plants, Genetically Modified; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011485:Protein Binding; D059748:Proteolysis / Q000528:radiation effects; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors
chemical_list: D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D056931:Cryptochromes; D046988:Proteasome Endopeptidase Complex; C533832:CIB1 protein, Arabidopsis; C103618:CRY2 protein, Arabidopsis; C450148:LKP2 protein, Arabidopsis; C410503:ZTL protein, Arabidopsis; C061553:ATP dependent 26S protease
keywords: gene expression; photomorphogenesis; protein degradation